1. Field of the Invention
The present invention relates to a thin film removing device and a thin film removing method for removing thin films from glass substrates for photomasks (reticles), flat display panels for flat panel displays (FPDs) and the like.
2. Description of the Related Art
Generally, a photomask fabricating process and a liquid crystal display fabricating process uses the photolithographic technique similar to that applied to semiconductor device fabrication for forming, for example, thin ITO films (indium tin oxide films) and circuit patterns. For example, the photolithographic technique applies a liquid resist to the surface of a substrate by a liquid resist application process to form a resist film on the substrate, exposes the resist film to an image of a circuit pattern by an exposure process, and forms a circuit pattern in the resist film by a developing process.
A spin coating method is widely employed in the liquid resist application process. The spin coating method holds a substrate on a spin chuck placed in a processing vessel, drops a liquid resist prepared by dissolving a photosensitive resin in a solvent on the substrate and rotates the spin chuck holding the substrate at a high rotational speed to form a resist film of a uniform thickness on the substrate by spreading the liquid resist over the surface of the substrate by centrifugal force.
When the resist film is formed by the liquid resist application process employing the spin coating method, there is some possibility that the uniformity of the thickness of the resist film deteriorates with time even if the resist film has the uniform thickness immediately after formation. For example, the liquid resist covering an edge part of the surface of the substrate is caused to rise by the agency of surface tension to increase part of the resist film covering the edge part of the surface of the substrate when centrifugal force disappears due to the stop of the spin chuck. In some cases, the liquid resist dropped on the upper surface of the substrate flows over the edges of the substrate to an edge part of the lower surface of the substrate and forms an unnecessary resist film on the edge part of the lower surface of the substrate.
If the resist film is formed on the edge part of the substrate in an irregular thickness, unnecessary parts of the resist film on the edge part of the substrate cannot be completely removed and remain on the substrate when a circuit pattern or the like formed in the resist film is developed. It is possible that the unnecessary remaining parts of the resist film affect adversely to the following processes or come off in particles during the transportation of the substrate.
Therefore, as mentioned in Patent document 1, namely, JP-A No. 2001-198515 (paragraph numbers 0061 to 0066, 0083 and 0084, FIGS. 3, 4, 6 and 10), the part of the resist film on the edge part of the substrate is removed by a thin film removing device called an edge remover. The thin film removing device has a thin film removing head, namely, a thin film removing means, to remove a part of the resist film from an edge part of the substrate. The thin film removing head moves along the edges of the substrate, jets a mixture of a solvent and a pressurized inert gas, such as nitrogen gas (N2 gas) to dissolve parts of the resist film on edge parts of the substrate in the solvent and to remove the parts of the resist film in a resist solution, and sucks the resist solution.
When carrying out the conventional thin film removing method, however, the mixture of the pressurized gas and the solvent spreads at the corners of the substrate in a range wider than that in which the pressurized gas spreads at the sides of the substrate, changing the flow of the pressurized gas for spraying the solvent and condition for sucking the resist solution. Consequently, the mixture cannot be jetted linearly, mists are formed, and corners of the resist film bulge in protrusions. Since a low suction acts on the corners of the resist film, mists formed around the corners cannot be satisfactorily sucked.